Wireless communication schemes allow wireless devices to communicate without the necessity of wired connections. Standards for wireless communication schemes are typically developed by organizations oriented toward a particular industry and then adopted within and/or across that industry. Standards may be developed and adopted in order to ensure, among other things, uniformity and interoperability within the industry, reduced development time, lower production costs, protection against obsolescence, and increased product quality and safety. Two such examples of wireless communication standards include Institute of Electrical and Electronics Engineers (IEEE) 802.11 and 802.16.
IEEE 802.11 includes the family of standards developed by the IEEE 802.11 committee, which established standards for Wireless Local Area Networks (WLAN). In part, the IEEE 802.11 family of standards defines methods of interoperability between wireless receivers and wireless transmitters. Wi-Fi™, a trademark of the Wi-Fi Alliance, is the term commonly used to refer to wireless communication and communication networks that are based on the IEEE 802.11 family of standards. As used herein, the term “Wi-Fi” will be used to refer to any communication network, system, apparatus, device, method, etc. that utilizes or is based on the 802.11 family of standards.
FIG. 1 is a block diagram of an exemplary Wi-Fi communication network. As shown in FIG. 1, an exemplary Wi-Fi network may include one or more transmitters, e.g., Access Points (AP) 110, including APs 110a, 110b, and 110c, one or more receivers, e.g., mobile subscriber stations (MSS) 120, including MSSs 120a, 120b, and 120c, and network 150.
The one or more APs 110 may be any type of communication device configured to transmit and/or receive communications based on the IEEE 802.11 family of standards, many of which are known in the art. In one exemplary embodiment, the one or more APs 110 may be connected to network 150. In addition, APs 110 may be configured to communicate with one or more MSSs 120 and other APs 110 using the communication protocols defined by the 802.11 family of standards. In one exemplary embodiment, one of APs 110 may serve as an intermediary between one or more MSSs 120 or other APs 110 and network 150. Network 150 may include, for example, any combination of one or more wide area networks (WAN), local area network (LAN), intranets, extranets, Internet, etc.
Each MSS 120 may be any type of computing device configured to transmit and/or receive data to and from APs 110 and/or other MSSs 120 using the communication protocols defined by the 802.11 family of standards. MSSs 120 may include, for example, servers, clients, mainframes, desktop computers, laptop computers, network computers, workstations, personal digital assistants (PDA), tablet PCs, scanners, telephony devices, pagers, cameras, musical devices, etc.
Each AP 110 may have a broadcast range within which AP 110 may communicate with one or more MSS 120 and other APs 110. Similarly, MSSs 120 may have a broadcast range within which MSS 120 may communicate with one or more other MSSs 120 and/or APs 110. Broadcast ranges may vary due to power levels, location, interference (physical, electrical, etc.). While the term “transmitter” is used to refer to AP 110 and the term “receiver” is used to refer to MSS 120, both AP 110 and MSS 120 may be configured to transmit and/or receive data.
The most commonly referenced amendments to the 802.11 family of standards include 802.11a, 802.11b, and 802.11g. 802.11a provides up to 54 Mbps transmission in the 5 GHz frequency band and uses an Orthogonal Frequency Division Multiplexing (OFDM) encoding scheme. 802.11b provides 11 Mbps transmission in the 2.4 GHz frequency band and uses Direct Sequence Spread Spectrum (DSSS) encoding. 802.11g provides up to 54 Mbps transmission in the 2.4 GHz frequency band and also uses OFDM encoding. In the United States and Canada, the allocated frequency for 802.11b/g is divided into 11 overlapping channels. Each channel is 22 MHz wide with a 5 MHz step to the next higher channel. While communication typically occurs in channels 1, 6, and 11 to avoid overlap, communication may occur within any of the channels.
The 802.11 family of standards requires the use of Distributed Coordinate Function (DCF), a form of Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA), a contention-based protocol. Generally, when MSS 120 seeks to transmit using CSMA/CA, it must first listen to the channel for a predetermined amount of time to check for activity on the channel. If the channel is sensed “idle,” MSS 120 may be permitted to transmit. If the channel is sensed “busy,” MSS 120 may have to defer its transmission until such time as the channel is sensed “idle.” In other words, in a Wi-Fi network, all MSSs 120 that seek to pass data to an AP 110 or another MSS 120 may compete for access on a random interrupt basis. This is commonly referred to as contention access.
As an optional access method, the 802.11 standard also defines the Point Coordinate Function (PCF). PCF is a contention-free access method that enables the transmission of time-sensitive information. With PCF, a point coordinator within AP 110 controls which MSSs 120 can transmit during any given period of time. For example, the point coordinator may first poll MSS 120a and, during a specified period of time, MSS 120a may transmit data. The point coordinator may then poll the next MSS 120 (e.g., MSS 120b) and, during a second specified period of time, MSS 120b may transmit data. The point coordinator may continue down the polling list, thereby allowing each MSS 120 connected to AP 110 a period of time during which it may send data.
AP 110 and MSS 120 may communicate by means of communication packets. These communication packets are called MAC “frames.” FIG. 2a illustrates an exemplary MAC frame format defined by the 802.11 family of standards. As shown in FIG. 2a, the MAC frame format may include the following fields: Frame Control (i.e., control data for the frame), Duration ID (i.e., duration of frame for data frames, identity of transmitting station for control frames), Address 1 (i.e., source address), Address 2 (i.e., destination address), Address 3 (i.e., receiving station address), Address 4 (i.e., transmitting station address), Sequence Control (i.e., sequence number and fragment number), Data (i.e., variable length message body), and FCS (i.e., 32-bit Cyclic Redundancy Check (CRC) value).
FIG. 2b illustrates an exemplary MAC Frame Control field defined by the 802.11 family of standards. As shown in FIG. 2b, the Frame Control field may consist of a number of sub-fields: Version (i.e., 802.11 version in use), Type (e.g., management, control, or data frame type), Sub-type (e.g., authentication frame, de-authentication frame, association request frame, association response frame, re-association request frame, re-association response frame, disassociation frame, beacon frame, probe frame, probe request frame, probe response frame, etc.), To DS and From DS (i.e., combination of values to indicate the distribution system combination), More Fragments (MF) (i.e., indication of more frame fragments to follow), Retry (i.e., retransmission), Power Management (PWR) (e.g., power save, active mode, etc.), More (i.e., indication of more frames to follow), Wired Equivalent Privacy (WEP) (i.e., indication of WEP data processing), and Order (O) (i.e., position of the current frame relative to other frames).
FIG. 3 is a signaling diagram of an exemplary embodiment of communication between one MSS 120 and one or more APs 110. As shown in FIG. 3, MAC frames may be used to “handover” or transfer communication for MSS 120 (e.g., MSS 120b) between a serving AP 110, e.g., AP 110a, and a target AP 110, e.g., AP 110b. Serving AP 110a may be an AP 110 currently providing service or communication to MSS 120b, and target AP 110b may be an AP 110 with which MSS 120b seeks to establish communication.
Generally, handover may be accomplished in two phases—a discovery phase and a re-authentication phase. In the discovery phase, MSS 120b may send a probe request (i.e., a MAC frame in which the Type and Sub-Type fields are set to indicate a probe request) to find potential target APs 110. The probe request may be broadcast on all channels to all APs 110 within range. In response, all APs 110 within range may send a probe request response (i.e., a MAC frame in which the Type and Sub-Type fields are set to indicate a probe request response). For example, if AP 110b is within range, AP 110b may respond to MSS 120b with a probe request response.
Once MSS 120b has identified target AP 110b for handover, a re-authentication phase may begin. To begin re-authentication, MSS 120b may send a re-association request (i.e., a MAC frame in which the Type and Sub-Type fields are set to indicate a re-association request) to target AP 110b. Through the use of Inter-Access Point Protocol (IAPP), which is based on 802.11f, notification of the handover may be made to serving AP 110a as well as to the rest of the network by target AP 110b. For example, AP 110b may communicate to AP 110a by sending a security block. AP 110a may acknowledge the security block, and AP 110b may then send a move request. AP 110a may acknowledge the move request, updating data tables and sending a move response.
Once the network processing is complete, AP 110b may send a re-association response (i.e., a MAC frame in which the Type and Sub-Type fields are set to indicate a re-association response) to MSS 120b. Once the re-association response is received, MSS 120b may begin regular communication with AP 110b. 
In this manner, wireless communication devices that operate according to the 802.11 family of standards, such as MSS 120b, may change physical locations yet maintain continuous communication with a network, such as network 150.
A second set of standards developed for wireless communication is IEEE 802.16. IEEE 802.16 includes the family of standards developed by the IEEE 802.16 committee, establishing standards for broadband wireless access. In part, the IEEE 802.16 family of standards defines the interoperability of broadband Wireless Metropolitan Area Networks (WirelessMAN). Generally speaking, WirelessMANs are typically large computer networks utilizing wireless infrastructure to form connections between subscriber stations. Wi-Max, a term defined and promoted by The Wi-Max Forum™, is commonly used to refer to WirelessMANs and wireless communication and communication networks that are based on the IEEE 802.16 standard. As used herein, the term “Wi-Max” will be used to refer to any communication network, system, apparatus, device, method, etc. that utilizes or is based on the 802.16 family of standards.
FIG. 4 is a block diagram of an exemplary Wi-Max network based on the 802.16 family of standards. As shown in FIG. 4, a Wi-Max network may include one or more transmitters, e.g., Base Stations (BS) 410, including BSs 410a, 410b, and 410c, one or more receivers, e.g., stationary subscriber stations (SS) 420, including SSs 420a and 420b, and mobile subscriber stations (MSS) 430, including MSSs 430a, 430b, and 430c. 
The one or more BSs 410 may be any type of communication device configured to transmit and/or receive communications based on the IEEE 802.16 family of standards, many of which are known in the art. In one exemplary embodiment, the one or more BSs 410 may be connected to a network 450. In addition, BSs 410 may be configured to communicate with one or more SSs 420, MSSs 430, and/or other BSs 410 using the communication protocols defined by the 802.16 family of standards. In one exemplary embodiment, BS 410 may serve as an intermediary between one or more SSs 420, MSSs 430, or BSs 410 and a network 450. Network 450 may be wired, wireless, or any combination thereof. Network 450 may include, for example, any combination of one or more WANs, LANs, intranets, extranets, Internet, etc.
SS 420 and MSS 430 may include any type of wireless client device configured to communicate with BS 410 and/or other SSs 420 and MSSs 430 using the communication protocols defined by the 802.16 family of standards. Each SS 420 and MSS 430 may include, for example, servers, clients, mainframes, desktop computers, laptop computers, network computers, workstations, personal digital assistants (PDA), tablet PCs, scanners, telephony devices, pagers, cameras, musical devices, etc. In one exemplary embodiment, SS 420 may be a Wi-Fi AP enabled to communicate with BS 410 using the communication protocols defined by the 802.16 family of standards.
Each BS 410 may have a broadcast range within which that BS 410 may communicate with SS 420, MSS 430, and one or more other BSs 410. Broadcast ranges may vary due to power levels, location, interference (physical, electrical, etc.). Similarly, each SS 420 and MSS 430 may have broadcast ranges within which that SS 420 and MSS 430 may communicate with one or more other SSs 420, MSSs 430 and/or BSs 410. Broadcast ranges may vary due to power levels, location, interference (physical, electrical, etc.). While the term “transmitter” is used to refer to BS 410 and the term “receiver” is used to refer to SS 420 and MSS 430, any of BS 410, SS 420, and MSS 430 may be configured to transmit and/or receive data.
In addition to the ability of each BS 410 to connect and communicate with SS 420 and MSS 430, each BS 410 may also connect and communicate with one or more other BSs 410 using a line-of-sight, wireless link using the protocols and standards defined by 802.16 family of standards. In other words, a Wi-Max network may provide two forms of wireless communication: a point-to-point (P2P) communication (e.g., between BS 410a and BS 410b) that operates at frequencies up to 66 GHz, and a point-to-multipoint (P2MP) communication (e.g., between BS 410 and one or more SSs 420 and/or MSSs 430) that operates in the 2.0 to 11.0 GHz range. In one exemplary embodiment, P2MP communication may include so-called Mobile Wi-Max (e.g., communication between BS 410 and one or more MSSs 430) Mobile Wi-Max is based on IEEE 802.16e-2005 and may operate in the 2.3 GHz, 2.5 GHz, 3.3 GHz, and 3.4-3.8 GHz spectrum bands.
The 802.16 family of standards specifies a MAC layer Time Division Multiplex (TDM) downlink coupled with a Time Division Multiple Access (TDMA) uplink. The 802.16 family of standards may also support both Time Division Duplex (TDD) and Frequency Division Duplex (FDD) operational modes. TDD is a technique in which the system may transmit and receive within the same channel, assigning time slices for transmit and receive mode. FDD, in contrast, may require two separate spectrums.
Transmission time may be divided into variable length frames. In an FDD system, the uplink (e.g., SS to BS or MSS to BS) and downlink (e.g., BS to SS or BS to MSS) sub-frames may operate on separate uplink and downlink channels. In a TDD system, each frame may be divided into a downlink sub-frame and an uplink sub-frame operating on a single channel.
FIG. 5 illustrates an exemplary MAC frame format based on the 802.16 family of standards. As shown in FIG. 5, the MAC frame format may include a DL-MAP and a UL-MAP. The DL-MAP is a directory of the slot locations within the downlink sub-frame. The UL-MAP is a directory of slot locations within the uplink sub-frame. Through the DL-MAP and UL-MAP sub-frames, BS 410 may allocate access to the channel for both uplink and downlink communication.
In contrast to a Wi-Fi network, a Wi-Max network may use a scheduling algorithm by which subscriber stations (e.g., BS 410, SS 420, MSS 430, etc.) may compete only once for initial entry to the network (i.e., the communication network provided by a serving BS 410 to subscriber stations within range). Once initial entry into the network is accomplished, access slots may be allocated by BS 410. The access slot may be enlarged or contracted, but the access slot remains assigned to a specific subscriber station, thereby precluding the use of the access slot by other subscriber stations. Thus, the scheduling algorithm may allow BS 410 to balance the access slot assignments among the application needs of one or more subscriber stations.
BS 410, SS 420, MSS 430 may communicate with each other through the use of MAC frames. MAC frames may be used to “handover,” or transfer communication, from a serving BS 410, e.g., BS 410a, to a target BS 410, e.g., BS 410b. A handover may occur when a subscriber station moves from within the broadcast range of one BS 410 to the broadcast range of another BS 410. Handovers may also occur when a BS 410 is disabled, suffers from a reduction in broadcast power, is removed from service, etc.
FIG. 6 is a signaling diagram of an exemplary handover between two BSs 410. When MSS 430 (e.g., MSS 430b) prepares to handover from a serving BS 410 (e.g., BS 410a) to a target BS 410 (e.g., BS 410b), serving BS 410a may transmit a Mobile Neighbor Advertisement (MOB_NBR_ADV) message to MSS 430b. Through the MOB_NBR_ADV message, MSS 430b may acquire information on one or more neighboring BSs 410. The MOB_NBR_ADV message may include a plurality of information elements (IEs), including, for example, a Management Message Type IE indicating a type of transmission message, an Operator ID IE indicating a network identifier, an N_NEIGHBORS IE indicating the number of neighbor BSs 410, a Neighbor BS-ID IE indicating IDs of neighboring BSs 410, a physical frequency IE indicating the channel frequency of neighboring BSs 410, and a TLV (Type, Length, Value) Encoded Neighbor Information IE providing other information related to the neighboring BSs 410.
MSS 430b may then transmit a Mobile Scanning Interval Allocation Request (MOB_SCN_REQ) message to the serving BS 410a. The MOB_SCN_REQ may be used by MSS 430b to initiate scanning of carrier-to-interference and noise ratios (CINRs) of pilot signals transmitted from neighboring BSs 410 and serving BS 410a. CINR scanning of pilot signals may be used to evaluate transmission power associated with the neighboring BSs 410 and serving BS 410a. The MOB_SCN_REQ message may include a plurality of IEs, such as, for example, a Management Message Type IE indicating a type of transmission message, a Scan Duration IE indicating a scan duration for which MSS 430b may scan CINRs of pilot signals received from neighboring BSs 410, and a Start Frame IE indicating a frame at which MSS 430b may start a scanning operation.
Upon receiving the MOB_SCN_REQ message, serving BS 410a may prepare and send a Mobile Scanning Interval Allocation Response (MOB_SCN_RSP) message to MSS 430b. The MOB_SCN_RSP message may include information which MSS 430b may use when scanning neighboring BSs 410, such as, for example, a Management Message Type IE indicating a type of transmission message, a Connection ID (CID) IE indicating a CID of the MSS that transmitted the MOB_SCN_REQ message (i.e., MSS 430b), a Scan Duration IE, and a Start Frame IE indicating a time at which a scanning operation may start. The Scan Duration may indicate a scanning duration for which the pilot CINR scanning is performed. In one exemplary embodiment, if the Scan Duration is set to “0” (Scan Duration=0), it may indicate that the scan request is rejected.
When MSS 430b receives the MOB_SCN_RSP message, MSS 430b may perform CINR scanning on the pilot signals received from serving BS 410a and any neighboring BSs 410. Based on the CINR scanning of the pilot signals, MSS 430b may determine if it should change from serving BS 410a to target BS 410b. 
If MSS 430b makes a determination to change from serving BS 410a to target BS 410b, MSS 430b may transmit a Mobile Subscriber Station Handover Request (MOB_MSSHO_REQ) message to serving BS 410a. The MOB_MSSHO_REQ message may include a plurality of IEs, including, for example, a Management Message Type IE indicating a type of a transmission message and the scanning results acquired by the MSS 430b. In addition, the MOB_MSSHO_REQ message may include the IDs of neighboring BSs 410, a service level that may be provided to the MSS 430b by the neighboring BSs 410, and an Estimated Handover Time (Estimated HO Time). Estimated HO Time may indicate the time at which the MSS 430b may select one of the neighboring BSs 410 as the target and begin handover. When serving BS 410a receives the MOB_MSSHO_REQ message transmitted by MSS 430b, serving BS 410a may detect a list of potential target BSs 410 to which the MSS 430b may be handed over.
Serving BS 410a may transmit a Mobile BS Handover Response (MOB_BSHO_RSP) message to MSS 430b in response to the MOB_MSSHO_REQ message. The MOB_BSHO_RSP message may include information on selected target BS 410b. The MOB_BSHO_RSP message may include a plurality of IEs, including, for example, a Management Message Type indicating a type of transmission message, Estimated HO Time, and information on potential target BSs 410. For example, the MOB_MSSHO_REQ message may include IDs for potential target BSs 410, and a predicted level of service that may be provided to MSS 430b by target BSs 410.
MSS 430b may then send a Mobile Handover Indication (MOB_HO_IND) message to serving BS 410a. The MOB_HO_IND message may include a plurality of IEs such as, for example, a Management Message Type IE indicating a type of transmission message, HO_IND_TYPE indicating whether the MSS 430b has accepted, rejected, canceled a handover to the selected target BS 410b, ID of selected target BS 410b, and HMAC tuple (i.e., Table Update Line Entry) used for authentication of the MOB_HO_IND message.
When serving BS 410a receives the MOB_HO_IND message indicating that MSS 430b has accepted the handover, serving BS 410a may release the connection to MSS 430b. Alternatively, serving BS 410a may retain the connection until it receives a report indicating completion of the handover to target BS 410b. After transmitting the MOB_HO_IND to serving BS 410a, MSS 430b may complete the remaining handover operation with target BS 410b. 
In this manner, wireless communication devices that operate according to the 802.16 family of standards, such as MSS 430b, may change physical locations yet maintain continuous communication with a network, such as network 450.
As shown above, the adoption of standards such as 802.11 and 802.16 may ensure that a device configured to operate according to one standard can communicate with any other device also operating according to that same standard. However, with the increased use of mobile wireless computing devices, there has been an increased need to facilitate handovers, or transfer of communication, between communication networks utilizing differing communication standards, so-called dual-model systems. As shown in FIGS. 4 and 6, however, handover standards and procedures between serving AP 110a and target AP 110b, which operate based on the 802.11 family of standards, may differ significantly from handover standards and procedures between serving BS 410a and target BS 410b, which operate based on the 802.16 family of standards.
In addition, further issues may arise when there is mutual signal interference between networks operating according to differing communication standards. For example, as shown in FIG. 7, certain Wi-Fi networks may operate in the 2.4 GHz frequency band while certain Wi-Max networks may operate in the 2.5-2.69 GHz frequency band. Thus, when a wireless client device needs to process Wi-Fi and Wi-Max information simultaneously, such as during a handover, there may be mutual signal interference due to the proximity of the frequency bands and the differences in transmission and reception power. Thus, there is an increased need for systems and methods for avoiding signal interference in dual-mode systems.
The disclosed embodiments are directed to overcoming one or more of the problems set forth above.